1. Field of the Invention
The present invention relates to a scroll pump having a pump head assembly that includes a stationary plate scroll and an orbiting plate scroll having stationary and orbiting scroll blades, respectively, in particular, the present invention relates to the means used to angularly synchronize stationary and orbiting scroll blades in a scroll pump.
2. Description of the Related Art
A scroll pump is a type of pump that includes a stationary plate scroll having a spiral stationary scroll blade, and an orbiting plate scroll having a spiral orbiting scroll blade. The stationary and orbiting scroll blades are nested with a radial clearance and predetermined relative angular positioning such that a pocket (or pockets) is delimited by and between the blades. The scroll pump also has a frame to which the stationary plate scroll is fixed and an eccentric drive mechanism supported by the frame. These parts generally make up an assembly that may be referred to as a pump head assembly of the scroll pump.
The orbiting scroll plate and hence, the orbiting scroll blade, is coupled to and driven by the eccentric driving mechanism so as to orbit about a longitudinal axis of the pump passing through the axial center of the stationary scroll blade. The volume of the pocket(s) delimited by the scroll blades of the pump is varied as the orbiting scroll blade moves relative to the stationary scroll blade. The orbiting motion of the orbiting scroll blade also causes the pocket(s) to move within the pump head assembly such that the pocket(s) is selectively placed in open communication with an inlet and outlet of the scroll pump.
In an example of such a scroll pump, the motion of the orbiting scroll blade relative to the stationary scroll blade causes a pocket sealed of from the outlet of the pump and in open communication with the inlet of the pump to expand. Accordingly, fluid is drawn into the pocket through the inlet. Then the pocket is moved to a position at which it is sealed off from the inlet of the pump and is in open communication with the outlet of the pump, and at the same time the pocket is compressed. Thus, the fluid in the pocket is compressed and thereby discharged through the outlet of the pump.
In the case of a vacuum-type of scroll pump, the inlet of the pump is connected to a chamber that is to be evacuated. Conversely, in the case of a compressor-type of scroll pump, the outlet of the pump is connected to a chamber that is to be supplied with pressurized fluid by the pump.
In any case, the predetermined angular position of the orbiting scroll blade relative to the stationary scroll blade must be provided and maintained within certain tolerances if the above-described intake and discharge operations are to be executed satisfactorily by the scroll pump. More specifically, the orbiting plate scroll must maintain a certain angular synchronization with the stationary plate scroll if seals created by and between the stationary and orbiting scroll blades are to form the pocket(s) stably, cause the volume of the pocket(s) to vary appropriately, and effectively cause the pocket(s) to move through the pump head assembly with the timing required relative to the inlet and outlet of the pump. To this end, the orbiting plate scroll must not rotate in excess of a certain amount about its own central axis while it orbits about the longitudinal axis of the pump head assembly.